This invention relates generally to governors and more specifically to a multi-unit governor control lever for resetting the governor to normal operation during start-up from a shut down or stopped position of the associated turbine or like apparatus controlled by the governor.
The present invention is illustrated with respect to a preferred usage thereof in a steam turbine where the governor acts to control inlet valve means disposed in the steam chest upstream from a safety trip valve in the inlet line feeding steam to the turbine.
Safety trip valves which are actuated responsive to any one or more of a plurality of adverse conditions potentially harmful to the continued operation of a steam or gas turbine act to cut off the flow of steam through the inlet passage for operating the steam or gas turbine. These single seated trip valves are adapted for use in single stage steam turbine systems because of their inherently low flow losses. However, they are subject to high unbalanced pressure forces and therefore present difficulties during the manual resetting of these valves particularly for example in steam turbines where the entering steam is at high temperatures and high pressures.
Further, those skilled in the art will recognize that the normal action of the governor causes the governor control lever to move the associated inlet valve means to the wide open position as the turbine speed drops when the safety trip valve is actuated to terminate delivery of steam through the inlet passage means to the turbine.
The problem heretofore presented is that when the safety trip valve is manually reset to the open position, if the governor does not respond reasonably promptly to the normal operating conditions desired, then the inlet valve means will cause the steam turbine to over speed and this will again trip the safety trip valve.
Some prior art devices have been developed to meet this problem as is shown in U.S. Pat. Nos. 2,257,279 and 1,786,942.
In the present invention this is accomplished by modifying the governor control lever to permit the inlet valve means upstream of the safety trip valve at the shut down or stopped position to be closed independently of the governor control lever operation and to enable the inlet valve means to move from closed to open position incrementally to bring the governor and its governor control lever back into normal operation, function and response to turbine operating conditions.
The governor control lever in accordance with the present invention is formed into a multi-section governor control linkage assembly wherein means are provided to adjust at least one section thereof relative the other to in turn first move the inlet valve means at the tripped, stopped or shut down position from open to closed position. Thereafter said means can be reversely operated to permit the inlet valve means to be moved incrementally from closed to open position so as to act as a throttling device for restarting the turbine and for bringing the turbine and its associated governor back to normal operating conditions.
Thus, the multi-section governor control linkage assembly in meeting the governor problem created when the safety trip valve is tripped as above outlined provides an inherent advantageous side effect in that with a relatively simple device, a manual control capability is established which heretofore as will be understood by those skilled in the art, had been provided by a more elaborate and expensive valve arrangement.
In addition to the throttling characteristic inherent in the governor control linkage assembly in accordance with the present invention, the construction effectively reduces the unbalanced forces acting across the safety trip valve. This occurs because after the safety trip valve is tripped and closed, and the inlet valve means is thereafter moved from open to closed position, the high temperature, high pressure steam trapped in the inlet flow passage between these elements will bleed off through clearances and/or orifices present in the safety trip valve thus balancing the pressure or forces acting across the valve head of the safety trip valve. Thus, manual forces required to reset the safety trip valve are materially reduced.
A third but still further important advantage which grows from the multi-section governor control linkage assembly in accordance with the present invention is that it can with a relatively few number of additional parts and connections be retrofitted to replace existing governor control levers and thus provide means for correcting this problem in existing turbine installations.